Field of the Invention.
This invention relates generally to apparatus located in an implantable medication infusion pump for quickly and easily detecting a condition adversely affecting medication delivery in the implantable medication infusion pump, and more particularly to such an apparatus and method for reliably detecting occurrences including an occluded catheter, the presence of air in the pumping mechanism, and the failure of the pumping mechanism.
Medication infusion pumps are generally known in the art for use in delivering a selected medication to a patient in a scheduled or preprogrammed manner. In recent years, such medication infusion pumps have been developed in compact form adapted for implantation into the body of a patient. They are used to deliver a specific medication such as insulin to the patient in discrete (but essentially continuous) doses over an extended time period.
An implantable medication infusion pump of this general type typically includes an internal medication reservoir for receiving and storing a supply of the selected medication in liquid form. Other components incorporated in the device include a power source (typically a battery), a miniature pumping mechanism, and associated electronic programmed control means for delivering the medication to the patient according to a prescribed schedule. For one illustrative example of an implanted or implantable medication infusion pump of this general type, see U.S. Pat. No. 4,573,994, to Fischell.
Implantable medication infusion pumps are normally equipped with an inlet port through which fluid medication can be supplied to permit periodic refilling of the pump reservoir. This inlet port is typically positioned and shaped for receiving a transcutaneous needle through which the fluid medication is supplied from outside the patient's body. Accordingly, the pump reservoir can be filled or refilled without requiring surgical removal from the patient's body, and further without requiring any other significant surgical procedure.
The output port of an implantable medication infusion pump is typically connected to the proximal end of a catheter. The distal end of the catheter is located in the abdominal cavity, where it may either be free-floating or implanted in the tissue of the omentum. If the distal end is to be free-floating, which is currently seen as the better technique, an intermediate portion of the catheter having a 90 degree bend therein is anchored to the peritoneal wall. If the distal end is to be placed into a fold in the omentum tissue, the tissue is sutured around the distal end of the catheter. The medication is thus delivered by the implantable medication infusion pump through the catheter to the body of patient.
While implantable, refillable medication infusion pumps constitute a major step forward in reliable and convenient administration of certain medications, there are several conditions which may be encountered which are difficult to detect, and which may impede the efficacious delivery of medication to the patient. The most significant of these problems is the problem of a partially or completely blocked catheter. This is typically caused by one of two blocking mechanisms: first, by tissue growth encapsulating substantially the entire distal end of the catheter to form a "sock;" or secondly, by deposits aggregating inside the lumen of the catheter to block or occlude the lumen of the catheter. Either of these conditions may result in the flow of medication from the catheter being partially or fully obstructed.
A catheter may become partially encapsulated or occluded, which will act to raise the pressure in the catheter when medication is being delivered. More infrequently, a catheter may become virtually fully encapsulated or occluded, essentially preventing the medication from flowing from the distal end of the catheter. Such a condition will defeat the intended purpose of the implanted system by substantially preventing it from delivering medication.
In delivering medications such as insulin, periodic relatively larger doses (boluses) are periodically supplied as needed (such as immediately before meals) in addition to an essentially continuous supply of the medication at a low rate (basal rate). With a partially obstructed catheter, the delivery of medication at the basal rate may not be a problem, while the delivery of a larger bolus may cause pressure to build to a point where delivery is significantly impeded. It will be recognized by those skilled in the art that nondelivery of medication due to a catheter obstruction thus represents a significant problem.
Another problem encountered by implantable medication infusion pumps is the presence of a gas bubble in the pumping mechanism. This is a particularly serious problem in medication infusion pumps which are incapable of pumping gas. Still another problem is that of pump failure, in which the pumping mechanism simply stops working for whatever reason. These problems, like the problem of catheter obstruction, may result in vital medication not being delivered to a patient.
At present, the lack of medication being delivered to a patient is generally detected by physiological measures. Such measures, for example, may include blood glucose analysis (for insulin), surgical procedures such as laparoscopy, or the use of an invasive pressure measuring technique such as a side port. These measures are all effective at diagnosis only significantly after the problem has been encountered for some time. In the case of a partially obstructed catheter, these techniques may not be successful in making a correct diagnosis.
A promising development has been the use of an acoustic sensor built into the pumping mechanism of the implantable medication infusion pump, which is taught in U.S. Pat. No. 4,985,015, to Obermann et al. (the '015 patent), which patent is hereby incorporated herein by reference. This device uses a piezo element located in the pumping mechanism to sense noise, with the noise sensed (or not sensed) providing information about medication infusion pump operation. The '015 patent teaches that the amplitude and timing of the acoustic signal present information useful to diagnosis of various pumping conditions.
Specifically, with regard to the timing of a "normal" signal the '015 patent teaches that an empty reservoir is indicated when the signal is greatly premature, and that air bubbles in the pumped fluid are indicated when the signal is slightly premature. With regard to the amplitude of the acoustic signal, the '015 patent teaches an amplitude or threshold discriminator which produces a signal when the medication infusion pump is operating properly, and no signal when the catheter is occluded. In the event of a catheter occlusion beginning to occur, there will be a signal when pumping is started, which signal will disappear when pumping at a high rate (read pumping a bolus).
Thus, the '015 patent teaches the use of a threshold detected acoustic signal, the timing and presence of which provides operational information on the system. This is certainly a significant improvement in the detection of the problems mentioned above. However, the system of the '015 patent has certain disadvantages representing opportunities for improvement in the art.
The '015 patent uses a threshold detection system which is incapable of detecting whether no signal detected is indicative of an occlusion or pump failure. This is highly significant, since it would be undesirable to perform a surgery to replace a catheter when the catheter is fine and the medication infusion pump is not operating properly.
It is accordingly the primary objective of the present invention that it provide an improved apparatus located in the implanted medication infusion pump and an associated method for detecting the problems mentioned above in the implanted medication infusion pump. The apparatus and method for detecting problems in the implanted medication infusion pump must be capable of discriminating between problems such as an encapsulated or occluded catheter and a nonoperational pumping mechanism. It is yet another objective that the apparatus and method of the present invention be capable of determining the presence of air in the system. The apparatus and method of the present invention must therefore allow a correct diagnosis of problems to be made with a high degree of accuracy while avoiding entirely an incorrect diagnosis which could result in the removal of a properly functioning system.
The apparatus and method for detecting problems in an implanted medication infusion pump must also avoid interference with spurious signals. The apparatus should not add significantly to the cost of manufacturing the implantable medication infusion pump. In addition, a means should be provided to enable the analysis to be tailored to individual patients, to better follow the conditions of these patients. It is also an objective that all of the aforesaid advantages and objectives be achieved without incurring any substantial relative disadvantage.